Januaey 31, 1902.] 



SCIENCE. 



177 



side and descending into the middle of the 

 receiver. It is the phenomenon which in- 

 terferes with the usefulness of narrow 

 tubular apparatus. 



4. As this subsidence of color bands in 

 benzine vapor is an observation of impor- 

 tance, I resolved to repeat the work under 

 more normal conditions. Accordingly I 

 used as my source of light the bright area 

 of the mantle of a "Welsbach burner, seen 

 through a small hole in the metallic screen 

 by an eye, .looking centrally through the 

 receiver containing saturated benzine vapor 

 and nucleated air. Punk nuclei replaced 

 the phosphorus nuclei. On exhaustion 

 (without nucleation) after standing over- 

 night, the coronas were white centered 

 fringed with brown, about as large as ordi- 

 nary lycopodium coronas seen under like 

 conditions. These large drops are a proof 

 of the relative absence of nuclei initially. 



After nucleation the first dense fogs 

 were vaguely annular during the first five 

 successive exhaustions, filtered air being 

 supplied between each. The next five ex- 

 haustions produced more nearly, finally 

 very fully stratified colors, in spite of the 

 point source of light. Shaking the receiver 

 violently at any time, so as to scatter the 

 liquid benzine within, always reproduced a 

 nearly perfect corona, which on standing 

 became distorted again, in color at least. I 

 now made special experiments, shaking the 

 receiver before each observation, bringing 

 out successive coronal effects* never as per- 

 fect as with water, however, always show- 

 ing the tendency to stratification. The 

 characteristic coronas succeeded each other 

 so rapidly that it would be difficult to make 

 them out. Nuclei, however, were still pres- 

 ent after over two hours, the eventually 

 white centered coronas showing a continued 

 shrinkage to smaller diameters in accord- 

 ance with the diminishing number of nuclei 



* These will be described for water vapor in a 

 subsequent paper. 



present. Twenty exhaustions did not re- 

 move them. 



Here, as above, therefore, the fleeting 

 character of the coronas, their tendency 

 to depart from the normal annular charac- 

 ter into stratification, the speed of descent 

 of the color bands, their rise upward on 

 exhaustion like a fog from a lake, are the 

 special characteristics of the colored cloudy 

 condensation occurring in benzine. To 

 these are to be added the striking axial 

 colors mentioned above. 



5. To explain the above phenomena in 

 their variation from the normal aqueous 

 corona, it is first necessary to account for 

 the more rapid subsidence of nuclei. I am 

 not aware of appreciable differences of vis- 

 cosity in the two vapors; but benzine has 

 the smaller latent heat of evaporation by 

 over seven times. Hence under identical 

 conditions of nucleation and for like ex- 

 haustions or like adiabatic cooling of a 

 given mass of saturated air, the drops 

 would be larger, the colors more advanced 

 in benzine than in water; and since the 

 square of radius is in question, this would 

 point to subsidence of the loaded nuclei in 

 benzine nearly four times more rapid. It 

 would also account for more rapid evapor- 

 ation or more fleeting colors, which is the 

 case. 



Again, if the loaded nuclei be regarded 

 as mechanical particles, the largest will 

 eventually be found in the lower strata, 

 the smallest in the upper strata, as in a 

 case of ordinary subsidence of suspended 

 matter in water. It is well known, more- 

 over, that smaller droplets wane, larger 

 droplets grow. Hence on increasing ex- 

 haustion condensation takes place flrst at 

 the bottom and last at the top, since the 

 smallest nuclei correspond to greatest 

 vapor pressure or difficulty in condensa- 

 tion, and since the largest nuclei have been 

 loaded with condensed liquid first, have 

 parted with it last, have had greater time 



